In many applications of ultrasound imaging controlled time delays of electronic signals are required. Many different methods of achieving time delays are possible, such as transmission lines, surface acoustical waves, and wave guides. However, one of the most common methods of achieving time delays is the use of lumped element delay lines. Lumped delay lines are comprised of discrete inductances and capacitances interconnected together in sections, such as the well-known T-section delay line.
Typically, a lumped element delay line is fabricated by first winding enamel coated wire on a bobbin with a given number of turns at a specified pitch (turns per inch), length-to-diameter ratio (L/D), and inductor-to-inductor spacings, and then connecting the delay line capacitors to the winding at specified locations. While lumped element delay lines have been highly successful, their previous manufacturing processes have had serious drawbacks. Specifically, since the delay line capacitors are connected to the winding only after the winding is completed, the enamel coating on the wire must be scraped away to allow an electrical connection with the capacitors. This scraping causes nicks and gouges on the underlying copper. Additionally, since the scraped area is usually tinned to facilitate the connection, insufficient scraping leads to poor tinning. Finally, the application of heat during tinning and soldering may cause the underlying bobbin to melt, thus adding contaminants to the solder joint. These effects all tend to reduce the resulting connection's reliability.
It is therefore clear that there has existed a need for a method of winding lumped element delay lines such that the delay line's inductors are wound continuously, but in a manner such that high reliability electrical connections with the winding is possible.